Wherever you turn in Davos, you see the World Economic Forum's modest motto: "Committed to improving the state of the world." Well, it needs it. So here's one practical step: the G8 should be expanded to G14, adding China, India, Brazil, Mexico, South Africa and Indonesia. Arbitrary? To be sure. Tactless? You bet. Deeply offensive to some important countries not on that list? Obviously - and they will cry havoc, foul and blue murder. But sometimes, if you're committed to improving the state of the world, you have to be a little brutal.

The dangers of climate change, nuclear proliferation, disease and poverty - not to mention the fragile state of globalised capitalism - demand a more credible and representative cast at the annual intergovernmental summit. As Asia rises, it is ever more absurd that the world's unofficial top table has a seat for Italy but not for China. The current lineup at the world's official top table, the UN security council, is not very satisfactory either, but it's also more difficult to change. The G8, by contrast, is a club that can simply decide to invite new members to join. That's how the G7 came to add Russia in the 1990s. No UN general assembly debate or ratification procedure is required. In principle, there's no reason why this decision could not be taken at the next annual summit, this summer in Japan. Like Nike, the G8 can just do it.

One objection to expanding the group is that it will lose intimacy, or "collegiality". But the fireside chats of the original "library group" of the early 1970s are already a thing of the distant past. Today's G8 summits are massive intergovernmental events, their every artful informality planned like a military operation. I'm told the American delegation to the last one, in Germany, had some 800 people. The qualitative difference between a lunchtime conversation of eight leaders and of 14 is not so great. The key deals will be made in smaller side-conversations anyway. The gain in representativeness, and therefore the global reach of commitments made on issues such as climate change, trade and aid, will more than compensate for the loss of pretended intimacy.

Another objection, a variant on the "collegiality" theme, is that the G8 has been a community of values. Expand it too far and you dilute the lifeblood of common values. But this has already happened with the admission of Russia. It's ridiculous to suggest that Vladimir Putin has more values in common with Gordon Brown than does Manmohan Singh, the prime minister of the world's largest democracy. If one wanted to keep this as a club of the world's leading liberal democracies, one should expel Russia and admit India in its place.

I have in the past been tempted by that idea; but it's not going to happen, and probably it shouldn't. The indispensable shared values therefore have to be rather minimal. Shall we say: committed to ensuring a future for humankind on this planet; a reasonable stability of the world economic system; and as much human dignity for as many human beings as the self-interested policies of states and the selfishness of voters will allow? To those minimal goals, even Putin's Russia can commit. And undemocratic China, too.

Apart from those two currently undemocratic giants, which themselves can evolve positively as well as negatively, the proposed expansion does not drastically reduce the domestic freedom base. It makes the club less western, but not necessarily less democratic. India, Brazil, South Africa and Mexico are all not merely electoral democracies but classified by Freedom House as free countries. And note that I propose as the major Islamic country for inclusion not Egypt or Saudi Arabia but Indonesia. Indonesia is both the world's largest Muslim country and a democracy, albeit of a ramshackle and imperfect kind.

So we have a rough and ready mix of criteria for membership: power and importance, above all, but also some degree of effective and answerable government (less in some cases, more in others), and some crude element of regional representativeness. Although there are more than 190 states in the world, these 14 states between them account for three-fifths of the world's population, more than two-thirds of its GDP, nearly three-quarters of its carbon dioxide emissions, and more than 80% of its defence expenditure. The regional tally would still reflect the heritage of western dominance, but it would now count Europe: 4 (plus European Union representatives in attendance), North America: 3, East Asia: 2, Latin America: 1, Africa: 1, Eurasia: 1, South Asia: 1 and South-East Asia: 1. An improvement, at least, on the current mix.

Some say you don't need to be so brutal. You could leave the current G8 as it is, or just add China and India but beef up the so-called G20 group of finance ministers, perhaps renaming it L20, to avoid total confusion and to reflect its enhanced role. (The L20 idea was originally pushed by the former Canadian prime minister, Paul Martin.) But this seems to me a fudge too far.

Others suggest you need different groupings for each issue, perhaps a C15 for climate change, a D23 for development, an E19 for energy security, and so on, all the way through to the Z99 for zoological diversity. In which case, our leaders would spend all their time attending international meetings, leaving no time left to run their countries. That would not improve the state of the world. Of course, other states need to be involved according to subject, but the fewer core groupings, the better.

While the process of UN reform grinds on, this reformed group of the world's most powerful and important countries (power and importance being not quite the same thing) should propose collective actions on climate change, world trade, development, energy security, HIV/Aids and Africa - to take a shortlist from Germany's G8 summit last year. It makes no sense at all to tackle an issue like climate change without the world's largest growing carbon emitters, China and India, at the table - which is why leaders of five of my six proposed new members were invited to attend part of that meeting, as the so-called "outreach five". So why not make it official?

Scepticism is plainly in order about what such meetings achieve, beyond declarations and promises. At the very least, the world's emerging great powers would have to think about, and take positions on, matters of wider responsibility which they might not otherwise confront. And the world's waning great powers could get used to listening to what the waxing ones have to say, and perhaps influence them too, before it is too late. Moreover, countries do actually make commitments at these summits. The independent G8 Research Group, based at the University of Toronto, monitors compliance on these commitments and produces league tables that show up the laggards. Embarrassment is worth something.

A G14 would be nothing like a world government. With time and luck, it might evolve into something that could be called, by very loose analogy with the 19th-century "Concert of Europe", a concert of world powers. Not a substitute for a reformed UN, but an essential complement to it. But which of today's G8 leaders will take up the challenge?